<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>改变表格边框的宽度</title>
</head>

<body>
    <table border="1" id="myTable">
        <tr>
            <td>100</td>
            <td>200</td>
        </tr>
        <tr>
            <td>300</td>
            <td>400</td>
        </tr>
    </table>
    <br>
    <input type="button" onclick="changeBorder()" value="修改边框">
    <script>
        function changeBorder() {
            document.getElementById('myTable').border = "10";
        }
    </script>
</body>

</html>